UBUNTU-CVE-2026-125108: Medium severity ubuntu/ruby-rack vulnerability
Rack is a modular Ruby web server interface. Prior to 2.2.25, 3.1.23, and 3.2.8, Rack::Multipart::Parser.parseboundary can skip a leading empty or quoted boundary parameter in a multipart Content-Type header and accept a later parameter. Rack can therefore parse a request body with a boundary that a conforming intermediary would not derive, allowing form fields or file uploads to reach an application without the intended proxy or web application firewall inspection. This issue is fixed in versions 2.2.25, 3.1.23, and 3.2.8.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Rackto a version that resolves this vulnerability.Fixed in 2.2.25 - Upgrade
Upgrade
Rackto a version that resolves this vulnerability.Fixed in 3.1.23 - Upgrade
Upgrade
Rackto a version that resolves this vulnerability.Fixed in 3.2.8
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments using Rack versions earlier than 2.2.25, 3.1.23, or 3.2.8 may be affected when they process multipart requests through an intermediary such as a proxy or web application firewall that derives the multipart boundary differently.
What does an attacker need to do to exploit it?
An attacker needs to send a multipart request with a Content-Type header containing a leading empty or quoted boundary parameter followed by another boundary parameter. Rack may use the later boundary while a conforming intermediary uses a different interpretation.
What is the practical security impact?
Form fields or file uploads can reach the application without receiving the intended proxy or web application firewall inspection. This can undermine controls that depend on intermediary inspection of multipart request contents.
How can the issue be remediated?
Update Rack to version 2.2.25, 3.1.23, or 3.2.8, as appropriate for the release branch in use.